A measuring arrangement for examining the surface finish and smoothness of a workpiece surface is disclosed in DE-AS 22 56 736. According to this prior art reference, a scanning beam is periodically moved over the surface of interest by means of a deflecting element. The scanning beam is reflected or scattered back to the same deflecting element and then deflected to a plurality of adjacent detectors, which output feedback signals representing the condition of the object surface.
U.S. Pat. No. 4,422,764 discloses an interferometer apparatus for measuring the microtopography of surfaces in two dimensions (surface roughness) using monochromatic light from a laser. The laser beam passes through a beam splitter 32 such that part of the beam impinges on reflector 38 and part impinges on the surface 12 of interest. The phase of the reflected beam is linearly varied by a means which applies a sawtooth wave to an electromechanical transducer on which the reflector is mounted. The beams from the reflector and the surface are recombined by the beam splitter and the interference fringe is detected, thus producing an alternating current signal the phase change of which is a measure of the topography of the surface.
Furthermore, GB-OS 2 106 654 discloses a measuring arrangement for observing variations in topography and/or material properties of the surface layer of a body. A capacitance probe 11 is scanned across the surface by means of a scan generator 14. Variations in the capacitance between the probe and the surface are converted into signals representing the topography and/or material properties.
The above-discussed references are all suitable for detecting the topography of a manufactured workpiece, which detection can be performed under controlled laboratory conditions. In a laboratory, the distance between the beam source and the object surface can be maintained constant. Also, in all of these prior art references the object is moved relative to a fixed detection system in order to carry out scanning. Thus, these references are not concerned with scanning systems, for example, mounted aboard vehicles, which themselves are moving and scan the object surface between a maximum and minimum scanning angle of the beam. Furthermore, these references neither disclose nor suggest a method and apparatus for automatically compensating for changes in the distance between the scanner and the object, changes in the maximum scanning angle, and changes in the oscillation frequency of the scanner.